Graphene mode-locked operation of Tm:YLiF and Tm:KYF lasers near 2.3 µm.

We report experimental demonstration of graphene mode-locked operation of ${{\rm Tm}^{3 + }}!:!{{\rm YLiF}_4}$Tm:YLiF (YLF) and ${{\rm Tm}^{3 + }}!:!{{\rm KY}3}{{\rm F}{10}}$Tm:KYF (KYF) lasers near 2.3 µm. To scale up the intracavity pulse energy, the cavity was extended, and double-end pumping was employed with a continuous-wave, tunable ${{\rm Ti}^{3 + }}!:!{\rm sapphire}$Ti:sapphire laser delivering up to 1 W near 780 nm. The extended ${{\rm Tm}^{3 + }}!:!{\rm KYF}$Tm:KYF laser cavity was purged with dry nitrogen to eliminate pulsing instabilities due to atmospheric absorption lines, but this was not needed in the case of the ${{\rm Tm}^{3 + }}!:!{\rm YLF}$Tm:YLF laser. Once initiated by graphene, stable uninterrupted mode-locked operation could be maintained with both lasers. With the extended cavity ${{\rm Tm}^{3 + }}!:!{\rm YLF}$Tm:YLF laser, 921 fs pulses were generated at a repetition rate of 17.2 MHz at 2304 nm. 739 fs pulses were obtained at the repetition rate of 54 MHz from the ${{\rm Tm}^{3 + }}!:!{\rm KYF}$Tm:KYF laser at 2340 nm. The corresponding pulse energy and peak power were 2.4 nJ and 2.6 kW for the ${{\rm Tm}^{3 + }}!:!{\rm YLF}$Tm:YLF laser, and 1.2 nJ and 1.6 kW for the ${{\rm Tm}^{3 + }}!:!{\rm KYF}$Tm:KYF laser. We foresee that it should be possible to generate shorter pulses at higher pump levels.